1. Field of the Invention
The present invention relates to a power transmission belt for transmitting rotational force, for example, between an engine output shaft and an air-conditioner, alternator, etc. in an automobile.
2. Description of the Related Art
A conventional power transmission belt is comprised for example of a belt body, on one side of which is formed a tooth portion, and cords embedded in the belt body.
In recent years, along with the improvements in engine performance, the rotational speed of the crankshafts has been rising. Further, larger loads have been generated due to use of the power for driving further auxiliary machinery. Therefore, the temperatures around where the power transmission belts are mounted have been becoming much higher.
Further, in applications for high performance engines, the rubber stock used for belt bodies has in recent years been changing from chloroprene rubber to hydrogenated nitrile rubber. Hydrogenated nitrile rubber is reputed to be superior in heat resistance, but when the rubber is subjected to repeated expansion and contraction at high speeds, the heat generated in the rubber itself (hereinafter referred to as the "internally generated heat") itself becomes large.
Due to the excessive heat, it has been difficult to produce drive transmission belts meeting engine requirements.
To solve this problem, it is necessary that the rubber itself have a strong resistance to heat deterioration. That is, the internally generated heat of the rubber should be small when the power transmission belt is driven at a high speed in a high temperature environment. Japanese Unexamined Patent Publication No. 63-270753 etc. disclose a technique of cross-linking hydrogenated nitrile rubber by zinc methacrylate and other metal salts of ethylenic unsaturated carboxylic acids and dicumyl peroxide or other peroxides so as to make it superior in heat resistance and give it rigidity along with elasticity, but this technique cannot be said to be sufficient.
Further, the service life of a power transmission belt is not dependent solely on the heat resistance of the rubber stock used for the belt body but is closely related with the material of the rubber stock and cords, the bonding strength of the two etc. These interact with each other.